Don't have any idea what Winchester has up its sleeve but there are a couple of points some of you seem to be overlooking in the wishes/dreams/hopes department.
First and most obvious is the pressure constraints attendant to rimfire cartridges. Second is the reason for bottle necking a cartridge case. It is done to provide more case capacity for a given caliber bore. More capacity equals more powder equals higher pressure. Third, the only way to overcome the pressure issue is to radically alter the form of the pressure curve. Forth and last, long range performance is as much about ballistic coefficients than muzzle velocity, or more when the relative range is very long. Once an aerodynamically efficient nose and base form for a bullet is established the only way to enhance BC is to add mass. Greater mass leads you back to problems with pressure, that being the essential weakness of the RF concept.
Don't get your hopes up too high.
